The rearrangement of immunoglobulin (and T cell receptor) genes is at many levels. Developmentally, in the B cell lineage, only proB and preB cells have the VDJ recombinase. The rearrangement substrate must be accessible, which presumably means it must be in an open chromatin configuration. Rearrangement signal sequences flanking the V,D and J gene joining partners must have the correct consensus sequence. Thus, one has some general picture of the rearrangement process, but many of the details of the molecular mechanism and its regulation are unknown. The specific aims of this proposal are to analyze in depth the requirements of immunoglobulin gene targets for rearrangement and the conditions for a correct rearrangement process in preB cells. The following experiments are planned: 1) Transgenic mice which carry a rearrangement test transgene will be studied to determine how the chromatin status of the transgene relates to its accessibility for correct rearrangement. This will include mapping a control gene(s) (the "strain specific modifier", SSM-1) which determines methylation and non-rearrangement in several transgenic lines and cloning of the SSM-1 gene; analysis of hybridomas and preB cell lines from the transgenic mice to explain the relationship between methylation of the transgene and its immunoglobulin gene specific rearrangement. 2) Determination of the effect of target gene methylation in vitro on immunoglobulin gene rearrangement. 3) Investigation of a specific suppressor of immunoglobulin gene rearrangement. 4) Study of the expression and function of a gene (p61) which encodes a DNA binding protein, possibly involved in immunoglobulin gene rearrangement. All the planned experiments will aid in the understanding of the expression and function of the partner genes involved in immunoglobulin gene rearrangement. Understanding this mechanism will provide a fundamental basis for the unraveling of many diseases involving the immune system, such as autoimmunities, infectious diseases, allergies and cancer.